Helicity-dependent showers and matching with VINCIA

We present an antenna shower formalism that includes helicity dependence for massless partons. The formalism applies to both traditional (global) showers and sector-based variants. We combine the shower with VINCIA's multiplicative approach to matrix-element matching, generalized to operate on each helicity configuration separately. The result is a substantial gain in computational speed for high parton multiplicities. We present an implementation of both sector and global showers, with min/max variations, and helicity-dependent tree-level matching applied through n <= 4 for V/H -> q (q) over bar + n partons and through n <= 5 for H -> n gluons. DOI: 10.1103/PhysRevD.87.054033